Fig 3. Histopathology. A closer look at the pulmonary infiltrate. Note the uniform sheets of large neoplastic round cells that infiltrate not only the perivascular/peribronchiolar spaces but also expand the parenchymal interstitium. There is mild congestion of the adjacent interstitium and increased numbers of vacuolated macrophages. H&E, x 200.

Final Diagnosis

Pulmonary lymphoma

Discussion

This is a large-cell, T-cell lymphoma. It is not entirely clear whether this represents primary or metastatic lymphoma in this lung. Given the apparent random distribution of the neoplastic infiltrate, I would not exclude metastatic disease. However, as no other primary lesions were observed/reported at the time of post-mortem and no neoplasia was evident in the submitted renal or liver samples, primary pulmonary lymphoma was considered a valid differential in this case.

Pulmonary involvement with lymphoma is very uncommon in cats but should be considered amongst the potential differentials for infiltrative miliary or consolidated lung lesions. Other clinical differentials worth considering would include other metastatic neoplasia, pulmonary infiltrates with eosinophils (PIE) and granulomatous or pyogranulomatous diseases (e.g. parasitic, fungal or mycobacterial).

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